Verification of component architectures using mode-based contracts

Abstract

We consider the problem of achieving a required level of confidence about safety-critical systems consisting of interacting components. Especially, we address restrictions in traditional A/G reasoning techniques which may cause false positives in contract compatibility analyses. Therefore, we introduce interface assertions, i. e., predicate logical formulae over the components' interfaces. We show how to compute interface assertions for architecture configurations based on the interface assertions of the corresponding components and show soundness and relative completeness of the method. Moreover, we introduce mode-based contracts, which - as a special kind of interface assertions - consist of dedicated assume and guarantee pairs. They provide a methodological guidance for developers and facilitate contract specification in contrast to e. g. traditional A/G reasoning. For this concept, we provide algorithms to check under-specification, over-specification, and the fulfillment of specifications. We also sketch how the checks can be operationalized using SMT solvers. Finally, an example demonstrates the approach.